For most people, forgetting a word, misplacing the keys, or becoming easily distracted is a normal part of aging, the result of general wear and tear on the billions of neurons in the brain. Changes in cognitive function—the ability to think, reason, and remember—also affect behavior and mood, and may contribute to psychiatric disorders like depression and anxiety, particularly in older adults.

It’s estimated that major clinical depression affects 2 to 3 million Americans aged 65 years or older, and milder depression strikes as many as one in six of this age group. Studies have shown that anxiety is even more common, affecting as many as 10-20 percent of the older population. Often the two go hand-in-hand, reducing overall health and quality of life.

“Late-life depression is very significant and extremely underestimated,” said Ruth O’Hara, PhD, an associate professor of psychiatry and behavioral sciences, who spoke at a presentation sponsored by the Stanford Hospital Health Library. “It often manifests as physical symptoms and so can be misdiagnosed and undertreated. It is not a normal aspect of typical aging.”

There are several aspects of cognition that are affected by aging, some more than others. The processes most impacted include:

Aging tends to cause structural changes in the brain, with a diminished hippocampus, reduced structural volume, and increased white matter lesions. And while it’s difficult to measure neuronal function, there are changes in neurotransmitters like serotonin, which is related to mood, and dopamine, which is involved in executive function.

“People with depression who develop dementia show greater problems with cognition,” Dr. O’Hara said. “And both memory performance and executive function are worse in older people who are depressed.”

Dr. O’Hara’s research looks at physiological function and neurophysiological changes related to cognitive decline and how they are related to anxiety and depression in older adults. Cognitive decline is not only a predictor of dementia, she said, it may also contribute to affective disorders such as late-life depression. There likely is a reciprocal relationship between affective and cognitive symptoms in late life. Anxiety, for example, is also related to lower cognition and can be as influential as depression: The more anxiety, the greater the cognitive decline.

Behavioral tests in a study of people age 60 to 89 years old showed that anxiety tends to affects inhibition and processing speeds, while depression impacts all aspects of cognition. Distractibility—the failure to inhibit—is the most significant cognitive change with age, she said, and the one that appears most related to emotion.

Other studies have shown that emotional regulation—techniques to keep emotions in check—may offer a means to stay in good mental health, and may lead to improvements in both memory and overall cognition.

“Emotional processing is associated with different patterns of diminished brain neurocircuitry in late-life depression and anxiety,” Dr. O’Hara said. Other factors include stress, sleep disturbances, diseases, and changes in neurotransmitters—chemical messengers that carry and modulate signals between neurons.

Research suggests that activities that exercise the brain and regular practice of emotional regulation strategies can actually improve cognitive abilities but must be done on a regular basis to show results. Best results may come from courses targeted to each individual, with structure, feedback, and assignments, rather than a self-directed routine.

These studies are important, she added, because they provide a window to understanding psychiatric disorders. “Cognitive dysfunction is a risk factor for the development of depression and anxiety in older adults and can impact response to treatment. It also may provide a potential target for treating these disorders.”

About the SpeakerRuth O’Hara, PhD, is an associate professor of psychiatry and behavioral sciences and director of the Veterans Affairs National Fellowship Program in Advanced Psychiatry and Psychology. Her work focuses on identifying the genetic risk factors and physiological markers of neurocognitive impairment in late-life disorders, including dementia and Alzheimer’s disease. Dr. O’Hara received her MA in experimental psychology from University College in Dublin, Ireland, and her PhD in experimental psychology from University of Southern California, Los Angeles. She worked at the UCLA Neuropsychiatric Institute before joining the Stanford faculty in 2000.